Xfinity Mistake turned nightmare for me!

I have contacted customer service at least 10-15 times over the past couple of months. Very disappointed in Xfinity. No one has been able to truly resolve my issue and I’m being charged for a phone that I do not have. I switched to Xfinity and brought my family’s lines over as well. That’s 4 lines total and I added the additional line because the phone was free. I agreed to trade in my phone along with my 3 family members phones and they were all iPhones. I was quoted $120 for 5 lines. Well when I received the new phone all were correct except for my phone. I did order correctly with the rep, however I was sent the wrong phone out of everyone. I didn’t notice until a couple days later and I had already switched services from AT&T. I had no choice but to call Xfinity and inform them that the wrong phone was sent for my line. Although it was a typo on the rep’s end, Xfinity made me pay for the correct phone I originally ordered. Once the new phone was received, I was told by Xfinity rep to return the trade in and include my incorrect phone in the same box as my trade it. She told me to do this to receive the trade in offer still. So I did. However my account continued to show 6 lines, instead of 5. Apparently the rep gave me incorrect instructions and the incorrect phone needed its own label! However I followed specific instructions! This has turned into months of being overcharged and numerous phone calls for a phone I returned a long time ago! They received all trade in phones and I was credited for each! Well the incorrect phone was in the same box as one of the trade ins so I know it was received but I guess somehow lost in the system which is not my fault! I can’t get real help or a real answer and I’m very frustrated and disappointed! How can I get real help!?